Python type system experiments.

Push the envelope as far as you can!
...and then give up and use cast(), because we don't have applicative
functors or higher kinded types

tests/test_signals.py

@@ -3,7 +3,7 @@ from typing import NamedTuple
 from unittest.mock import MagicMock
 from gears import Gear
 from gears.connections import connect
-from gears.effect import effect_of, effect_of_2
+from gears.effect import effect_of
 
 
 def test_get_set():
@@ -35,7 +35,7 @@ def test_effect_of_2():
 
     last_arg: tuple[str, int] | None = None
 
-    @effect_of_2(g1, g2)
+    @effect_of(g1, g2)
     def value_changed(v1: str, v2: int):
         nonlocal last_arg
         last_arg = (v1, v2)